Field
A method and apparatus for detecting a condition of an implantable shunt device, more specifically, for detecting a location of a shunt malfunction. Other embodiments are also described and claimed.
Background
A shunt is a surgically implanted device that allows for movement of fluid from one part of the body to another. In the case of a cerebral shunt, the shunt diverts cerebrospinal fluid (CSF) from the brain or spine into various body cavities such as the peritoneum, plural space, heart, etc. CSF is produced by the brain and circulates from the brain to the spine and then gets absorbed in the veins. A normal adult produces between 15-20 cc of CSF per hour. CSF acts as a “cushion” or buffer for the cortex, providing a basic mechanical and immunological protection to the brain inside the skull and serves a vital function in cerebral autoregulation of cerebral blood flow.
When the body fails to properly absorb the CSF, an abnormal accumulation of CSF occurs in the ventricles or cavities within the brain resulting in a medical condition known as hydrocephalus. A cerebral shunt may be implanted within the patient's brain to help drain the CSF and redistribute it to a different body region for absorption. Cerebral shunts typically consist of three parts: a proximal catheter, a valve and a distal catheter. The proximal catheter is inserted into the brain ventricle, which is a site of CSF build up, while the distal catheter is positioned within any body tissue having enough epithelial cells to absorb the incoming CSF. Typically, the distal catheter is positioned within the peritoneum (where the abdominal organs are located) or the pleural space outside the lungs or the atrium of the heart. The pressure differential between the high pressure brain region and the lower pressure abdomen, lung or atrial region causes the CSF to be drawn into the proximal catheter and out the end of the distal catheter.
The valve is between the proximal catheter and the distal catheter and is typically positioned behind the ear. The valve is used to control the amount of CSF flowing from the brain to the stomach. When a pressure within the brain increases, a pressure level at the valve increases above a threshold level (e.g., a low, medium or high pressure) causing a gate within the valve to open. CSF can then flow from the brain to the abdomen thereby reducing the pressure level within the brain. Once the pressure drops below the threshold level at the gate, the valve closes the gate so that CSF flow is stopped. In a fixed pressure setting valve, the pressure threshold level of the valve may be preset prior to placement of the shunt within the body. Alternatively, the valve may be adjustable such that the threshold level can be changed electronically using a device outside the body without having to remove the shunt.
A working cerebral shunt is critical to patient survival. Cerebral shunts, however, often fail. The failure can be either mechanical or infectious. In addition, a patient may report symptoms consistent with shunt failure, but in actuality, the shunt is working fine. Since the shunt is implanted within the patient's body, it is difficult to determine the condition of the shunt and, when there is a failure, which part of the stunt requires repair. A computed tomography (CT) scan can be performed to determine whether the brain is draining properly, but sometimes a CAT scan is inconclusive because the desired region cannot be viewed properly. In addition, the portion of the shunt in need of repair cannot typically be identified from the CAT scan and CSF flow cannot be evaluated. Similar problems arise using x-ray techniques. Other techniques to assess CSF flow through the shunt, such as a radionuclide shuntogram or needle aspiration of the valve reservoir are invasive, unreliable and non-informative. The patient must therefore undergo an exploratory shunt surgery so that the surgeon can examine the shunt directly. Exposing the shunt, however, comes with subjecting the patient to surgical risks and, in addition, a high infection risk to the patient. In particular, each time a shunt is exposed, there is a 30% chance that within 3 months the patient will get an infection.